The role of central monoamines in the positive reinforcing effects of affective touch

Rationale Affective touch can produce positive emotional states and serves as a critical component of social bonding. Although the circuitry of affective touch has been well characterized, the role of central monoamines in the functional consequences of affective touch has not been systematically examined. Objectives The objective of this study was to examine the role of monoamines in the positive reinforcing effects of affective touch Methods Male and female rats were treated with selective monoamine reuptake inhibitors (GBR 12909, atomoxetine, fluoxetine) and nonselective monoamine releasers/reuptake inhibitors (amphetamine, cocaine, MDMA) and placed into an apparatus divided into two equally sized areas. When rats were in the “touch” area, they were “petted” by a blinded experimenter; when rats were in the “no touch” area, they were left undisturbed. All drugs were tested across a 10-fold dose range, and saline and oxytocin were tested as negative and positive controls, respectively. Results Affective touch served as a positive reinforcer as indicated by a preference for the “touch” area. Oxytocin, the nonselective monoamine reuptake inhibitor cocaine, and the nonselective monoamine releaser amphetamine robustly increased the reinforcing effects of touch. To a lesser degree, the selective dopamine reuptake inhibitor GBR 12909 increased the reinforcing effects of touch, whereas the nonselective monoamine releaser/reuptake inhibitor MDMA decreased the reinforcing effects of touch. Conclusions These data suggest that drugs that increase synaptic dopamine, particularly those with high addiction liability, increase the positive reinforcing effects of affective touch. These data also suggest that MDMA may not reproduce in rodents the entactogenic effects commonly reported in humans and some nonhuman primate studies.